Berl JL & Black JM 2011. Vigilance Behaviour of American Wigeon

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Vigilance behaviour of American Wigeon Anas americana foraging in pastures

JACOB L. BERL1 & JEFFREY M. BLACK1*

1Waterfowl Ecology Research Group, Department of Wildlife, Humboldt State University, Arcata, California 95521, USA. *Correspondence author. E-mail: [email protected]

Abstract Observations were made of feeding American Wigeon Anas americana to assess their vigilance levels in relation to foraging location. American Wigeon increased vigilance levels: 1) while foraging on land compared to on water, 2) while grazing progressively further away from a water source, and 3) after being on land for long periods of time. Vigilance patterns were nearly identical to those recorded for Eurasian Wigeon Anas penelope in earlier studies. Males were more vigilant than females when foraging on land. This study contributes to understanding the importance of ephemeral pond habitats to grazing American Wigeon, which are used as anti-predator refuges by actively feeding flocks.

Key words: anti-predator behaviour, distance from water, grazing, head-up posture, scanning.

Relationships between vigilance and (Owen 1973; Kanel 1981; Owen & Thomas foraging are fundamental in waterfowl 1979; Mayhew 1987; Mayhew & Houston behavioural ecology because they imply 1989; Jacobson & Ugelvik 1994a,b; Larsen trade-offs between alert behaviour and 1996; Guillemain et al. 2003; Portugal foraging effort (Lazarus 1978; Lazarus & & Guillemain 2011), yet there have been Inglis 1986; Poysa 1987; Guillemain et al. no comparable studies of its Nearctic 2002a, 2007a). Besides monitoring mates, counterpart, American Wigeon Anas competitors and other flock members, americana. vigilant individuals scan the area for American Wigeon wintering and potential predators (Pulliam & Caraco migrating through coastal northern 1984; Elgar 1989; Lima & Dill 1990; Owen California occupy similar wetland habitats to & Black 1990; Caro 2005; Beauchamp Eurasian Wigeon occurring in Europe 2009). The feeding ecology and vigilant (Lovvorn & Baldwin 1996), and walk onto behaviour of Eurasian Wigeon Anas penelope adjacent saltmarsh or pastures to graze have been well documented in Europe vegetation. American Wigeon, like Eurasian

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Wigeon, are faced with the challenge of Methods foraging in an inherently “riskier” environment (e.g. increased mammalian Observations of actively feeding American predation risk and reduced response time) Wigeon took place on ephemeral ponds in when on land and away from water (sensu grass pastures near Arcata, California, USA Mayhew & Houston 1989; Portugal & (40°N, 124°W). The majority (90%) of Guillemain 2011). Moreover, American observations were made at three ephemeral Wigeon are confronted with predation risks ponds in the Jacoby Creek/Gannon Slough similar to those of Eurasian Wigeon while Wildlife Area, a pastureland preserve 1 km foraging on dry land, in that they occupy southeast of Arcata, along the western habitats with analogous mammalian and shore of Humboldt Bay, California. The avian predators. remaining observations were made at two Vigilance in waterfowl has been shown to ephemeral waterbodies on nearby (<10 km be highly variable and can be influenced by away) farmland pastures which were a variety of factors, including: 1) sexual commonly used by American Wigeon. differences (Inglis 1977; Mayhew 1987; Habitat type consisted of cattle Bos taurus Black & Owen 1989a,b), 2) distance from a grazed pasture and seasonally flooded water source (Mayhew & Houston 1989), 3) freshwater ponds and marshes (Barnhart et time of year (Portugal & Guillemain 2011), al. 1992). The most common pasture plant 4) flock size and position within the flock species included Velvetgrass Holcus lanatus, (Inglis & Lazarus 1981; Mayhew & Houston Bentgrass Agrostis sp., Italian Ryegrass 1989; Roberts 1996; Black et al. 1992), 5) pair Lolium mulliforum, Orchardgrass Dactylis and family status (Lazarus & Inglis 1978; glomerata, Festuca Festuca sp., Clover Trifolium Black & Owen 1989a; Guillemain et al. 2003, sp., and Buttercup Ranunculus sp. (Long 2007b), 6) presence of other species 1993). Vegetation height was kept short (e.g. (Jacobson & Ugelvik 1994b; Larsen 1996), < 8cm) by intensive cattle grazing. Vigilance 7) feeding style/method (Guillemain et al. behaviour (proportion of time with head-up 2002b) and 8) visual fields (Guillemain et al. during focal bird observations) did not 2002a). differ across sites (Kruskal-Wallis H2 = 1.66, This study aimed to determine whether n.s.), so data were lumped for the larger American Wigeon displayed similar vigilant analysis. behaviour to their European counterparts. Focal bird observations were conducted In particular, variation in American Wigeon from 31 January 2011 to 24 March vigilance levels was examined for birds 2011, coinciding with peak American feeding on different habitats (i.e. on Wigeon migration in Northern California land versus water), as the birds grazed (Hitchcock et al. 1993) and the end of the progressively further from a water source waterfowl hunting season. Procedures for into areas of higher biomass, and also focal bird observations followed the after grazing on land for long periods of methods of previous vigilance studies on time. Eurasian Wigeon (see Mayhew 1987;

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Mayhew & Houston 1989), including a which did not affect birds’ feeding variable observation time, between 1–3 min behaviour. (average = 96 s). Individual focal birds were Disturbance events (e.g. anthropogenic viewed continuously for the duration of disturbance or overflying raptor) would each behavioural observation, which were stimulate “snap back” (quickly run or fly) carried out using a 20–60× spotting scope flock responses to the nearest waterbody. and 8× binoculars from distances of 75–200 The timing of “snap back” events (i.e. total m. Foraging in pastures was characterised as time away from water) was recorded, grazing, while foraging on water consisted although their cause was not determined. predominantly of dabbling, but also Additionally the length of time an individual upending and picking items from the had been foraging on land was recorded at water surface. Vigilance was described as: the start of each focal observation. 1) proportion of an observation period Food supply was recorded by clipping all with head-up (time vigilant / length of above ground vegetation within an 8 × 8 cm observation), 2) head-up rate (number of frame at the 6 distance categories every two head-ups / length of observation; weeks. Green biomass was separated from converted to head-ups/s), and 3) scanning brown/dead material, desiccated at 60º C duration (time vigilant / number of head- for 24 h, weighed immediately upon ups). A head-up was recorded when an removal from oven, and converted to g/m2. individual stopped feeding and raised its The influence of distance from water on head and neck above parallel. All time vigilance levels was tested using Kruskal- recordings were made using standard Wallis analysis of variance. Differences in stopwatches. vigilance between foraging situation and To reduce the likelihood of double sexes were analysed by Mann-Whitney U sampling, the number of focal observations tests. Spearman rank correlations were was restricted to 10 per study site per employed to test the relationship between observation day while alternating between vigilance and time away from a water source. males and females. With an average flock One-way ANOVA was used to test variance size of 99 individuals (range = 24–280 in green biomass and time away from a birds), this limited sampling to < 10% of water source in relation to distance birds within the flock each day. In all cases, categories. Correlation coefficients and line the centremost bird in view of appropriate slopes were determined for plots of these sex was selected for focal observation. relationships. To account for effects of To assess vigilance at varying distances flock size on vigilance, observations from water, all on-land focal observations were made from flocks with at least 20 were placed into “distance from water” individuals (see Mayhew 1987) (range = categories, recorded against 10 cm high 24–280, mean = 99, s.e. ± 5.5) and we wooden stakes at intervals of 0–5 m, 5–10 checked that vigilance was not related to m, 10–15 m, 15–20 m, 20–30 m, and 30–40 flock size (Spearman rank correlation: m to ensure accurate distance records but proportion vigilant, r117 = 0.106, P = 0.24,

©Wildfowl & Wetlands Trust Wildfowl (2011) 61: 142–151 Vigilance in American Wigeon 145 n.s.). In consideration of animal safety water bodies in terms of proportion and welfare, this work was approved by vigilance (H6 = 70.87, P < 0.001), rate of Humboldt State University Institutional head-ups (H6 = 61.18, P < 0.001), and Animal Care and Use Committee Protocol scanning duration (H6 = 29.83, P < 0.001) (IACUC Protocol No. 10/11.W.32.E). (Fig. 2a,b,c). Individuals were more vigilant Means are given ± s.e. values throughout. with increasing time on land away from

water bodies (proportion vigilance, r98 = Results 0.44, P < 0.001); time away from water One hundred and nineteen focal corresponded positively with “distance from observations of actively feeding American water” categories (F6,98 = 11.25, P < 0.001) Wigeon were completed over the course of and the amount of available green biomass the study. The ducks were more vigilant increased with distance from water (F6,16 = while foraging on land than water (U117 = 4.93, P < 0.01, Fig. 2d). The median length 1764, P < 0.001, Fig. 1). Vigilance levels of time flocks would graze before a “snap significantly increased with distance from back” to water was 9 min 44 s (s.e. ± 58 s;

0.16 50 0.14 Male Female 50 0.12

0.10

0.08

0.06 9 10 0.04

Proportion of time vigilant 0.02

0.00 Pond Pasture Foraging habitat

Figure 1. Proportion of time that American Wigeon were vigilant (mean ± s.e.) in relation to foraging habitat and sex, in ephemeral ponds and pastures near Arcata, California, USA, 31 January–24 March 2011. American Wigeon displayed significantly higher proportion vigilance while foraging on pastures than on water (U117 = 1764, P < 0.001). Males were significantly more vigilant while foraging in pastures (U98 = 1026, P < 0.001), while females were significantly more vigilant while foraging on ponds (U17 = 29, P < 0.05).

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(A)

r = 0.974

(B)

r = 0.906

(C)

r = 0.908

On water 0-5 5-10 10-15 15-20 20-30 30-40 Distance from water (m)

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(D)

r = 0.708

On water 0-5 5-10 10-15 15-20 20-30 30-40 Distance from water (m)

Figure 2. American Wigeon vigilance and biomass assessment in relation to distance from ephemeral waterbodies in grassland pastures near Arcata, California, USA, 31 January–24 March 2011. (A) Proportion of time vigilant (mean ± s.e.) for American Wigeon foraging on water, and at progressively 2 further distances from a water source (y = 0.0324x + 0.0074, r 119 = 0.974, P < 0.001). (B) Rate of “head-ups” (mean ± s.e.) while foraging on water and at progressively further distances from water (y = 2 0.059ln(x) + 0.0508, r 119 = 0.906, P < 0.001). (C) Scanning duration (length of individual head-ups) in 2 relation to distance from water (y = 0.1427x + 0.5345, r 119 = 0.908, P < 0.001). (D) Amount of green biomass per m2 (mean ± s.e.) available to grazing American Wigeon at different distances from water (y 2 = 0.139ln(x) + 0.2605, r 21 = 0.763, P < 0.01). n = 100; range = 1 min 25 s – 23 min 33 s). parallels those of Mayhew (1987) and While foraging on land, in potentially riskier Mayhew & Houston (1989) who quantified environments, the proportion of time being a similar response in Eurasian Wigeon vigilant (Fig. 1) and the rate of head-ups foraging on coastal pastures in Scotland.

(U98 = 1420, P < 0.05) was significantly Furthermore, this behaviour has been higher for males than females. documented for other waterbirds, as Schütz & Schulze (2011) found for spring-migrating Discussion Ruffs Philomachus pugnax in eastern Austria, Vigilance behaviour by individual American which increased their scan rates while Wigeon increased significantly as they foraging on terrestrial compared to semi- moved further away from water. Increased aquatic habitats. In coastal northern investment in head-up scanning behaviour California, grazing American Wigeon rather than head-down grazing seemed to be apparently also used pond habitats for safety, due to a perceived increase in predation risk as vigilance levels substantially decrease once when out of the water. This suggestion they “snap back” into the water. Moreover,

American Wigeon became more vigilant shared habitat, rather than an organised after being away from water for long periods mixed-species flock. American Wigeon of time. Time away from water appeared to vigilance increased slightly in the presence have such an impact on perceived predation of the geese (12.3% ± 1.4%) compared to risk that all flock members would stop situations without geese (9.3% ± 0.7%), grazing after extended periods away from although the difference was not significant water and return to ponds in the absence of (U117 = 495, P = 0.08, n.s.). a disturbance stimulus, occurring in 5 out of Male American Wigeon were more 21 observations (24%) when they were on vigilant than females while grazing on land land longer than 10 min. Regrouping flocks and seem to reduce investment in vigilance on the pond would then return to land for a when in the water. Although pairing status renewed grazing bout. Foraging flocks of was not evaluated in this study, it is American Wigeon were rarely observed in likely that the observed increase in male pastures lacking water bodies. These vigilance can be attributed to paired males observations corroborate Mayhew & providing mates with enhanced foraging Houston’s (1989), suggesting water bodies opportunities. Mayhew (1987) and Portugal act as refuges for wigeon to escape predation & Guillemain (2011) found increased or disturbance. Grazing on land has long vigilance levels in male Eurasian Wigeon been regarded as a “risky” foraging method compared to females while foraging on land in waterfowl (e.g. Mayhew & Houston 1989; in potentially “riskier” situations. It is likely a Portugal & Guillemain 2011). Overall, portion of increased male vigilance at American Wigeon vigilance rates (time spent further distances from water resulted in vigilant: average = 9.7% ± 0.7%, n = 119) “low-cost vigilance” due to increased food were remarkably similar to those observed in handling time in areas of high grass biomass Eurasian Wigeon (c. 10%) (Mayhew 1987; (Portugal & Guillemain 2011), which would Portugal & Guillemain 2011). allow males to maximize foraging efficiency Larsen (1996) suggested that Eurasian and alert behaviour. It is also possible that a Wigeon dependence on water for anti- portion of the increased scanning behaviour predator protection can be offset by the was directed at potential competitors in presence of large-bodied geese. American areas with different food densities. Grass Wigeon fed on eelgrass Zostera marina near biomass was reduced from repeated Black Brant Branta bernicla nigricans on nearby depletion by ducks at distances that were Humboldt Bay, but usually grazed in single closer to the water (see Mayhew 1987; species flocks on pastures (JLB & JMB, pers. Portugal & Guillemain 2011). Variation in obs.). During this study Aleutian Cackling vigilance by flock members has been Geese Branta hutchinsii leucopareia were described in habitats with different amounts recorded feeding near (within 100 m) and types of food for a range of waterfowl American Wigeon flocks on 12% of the species (e.g. Scott 1980; Black & Rees 1984; observations. However, these interactions Black & Owen 1989b; Kotrschal et al. appeared to be chance inter-species use of 1993).

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Photograph: American Wigeon taking flight, by Leslie Scopes Anderson.